Inspecting a multilayer sample

ABSTRACT

Inspecting a multilayer sample may include receiving, at a beam splitter, light and splitting the light into first and second portions; combining, at the beam splitter, the first portion of the light after being reflected from a multilayer sample and the second portion of the light after being reflected from a reflector; receiving, at a computer-controlled system for analyzing Fabry-Perot fringes, the combined light and spectrally analyzing the combined light to determine a value of a total power impinging a slit of the system for analyzing Fabry-Perot fringes; determining an optical path difference (OPD); recording an interferogram that plots the value versus the OPD for the OPD; performing the previous acts of the method one or more additional times with a different OPD; and using the interferogram for each of the different OPDs to determine the thicknesses and order of the layers of the multilayer sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 16/174,053, filed on Oct. 29, 2018, which is a continuation of U.S. patent application Ser. No. 15/486,146, filed on Apr. 12, 2017, the disclosures of which are incorporated herein by reference in their entirety.

FIELD

The embodiments discussed in this disclosure relate to inspecting a multilayer sample.

BACKGROUND

During an automated manufacturing process, a multilayer sample of material, such as a multilayer wafer, may be inspected using conventional inspection systems to determine the overall thickness of the multilayer sample and to determine thicknesses of the various layers. During the automated manufacturing process, while the composition of each of the layers is often known, the order of the layers, and the corresponding orientation of the layers, is often unknown.

For example, during an automated manufacturing process, a multilayer wafer may have a silicon layer and a silicon dioxide layer, and the multilayer wafer may need to be oriented with the silicon layer on top to allow the silicon layer to be ground down during the automated manufacturing process to a specific thickness. Therefore, a conventional inspection system may be positioned above the multilayer wafer to inspect the multilayer wafer as it travels through the automated manufacturing process in order to measure the thickness of the top silicon layer to verify that the silicon layer is successfully ground down to the specific thickness. In this example, however, the multilayer wafer may inadvertently become turned upside down during the automated manufacturing process such that the silicon layer, which should be on the top to be exposed for grinding down, ends up on the bottom. While the conventional inspection system may be able to determine that the multilayer wafer has a top layer and a bottom layer, and may be able to determine the thicknesses of the top layer and the bottom layer, the conventional inspection system may be unable to determine which of the top and bottom layers is the silicon layer and which is the silicon dioxide layer.

In another example, during an automated silicon wafer thinning and packaging process, the detailed structure of a multilayer wafer may be unknown. In this automated process, identifying a remaining silicon thickness may involve determining a thickness of: the lowest layer of the structure if the multilayer wafer resides on grinding tape, the second-lowest layer if the multilayer wafer resides on dicing tape, or the third-lowest layer if the multilayer wafer resides on Die Attachment Film (DAF) tape attached to dicing tape. The exact thickness of the remaining silicon may be an important parameter for heat transfer in modern semiconductor devices. While a conventional inspection system may be able to determine that the multilayer wafer has multiple layers, and may be able to determine the thicknesses of the layers, the conventional inspection system may be unable to determine the compositions and order of the layers. For example, a conventional inspection system may be unable to determine the thickness of a particular layer of a multilayer wafer, such as the layer that is intended to be the lowest layer of the multilayer wafer.

Therefore, conventional inspection systems may be unable to correctly identify differences in the compositions of different layers of a multilayer sample during an automated manufacturing process. This inability of conventional inspection systems may result in undetected problems with the order of the layers in a multilayer sample, and the corresponding orientation of the layers, such as undetected upside-down multilayer samples, resulting in manufacturing defects during the automated manufacturing process.

The subject matter claimed in this disclosure is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one example technology area where some embodiments described in this disclosure may be practiced.

SUMMARY

One example embodiment may include a method for inspecting a multilayer sample. The method may include emitting, from a broadband light source, light over single mode optical fiber. The method may also include receiving, at a beam splitter, the light and splitting, at the beam splitter, the light into first and second portions. The method may further include directing, from the beam splitter, the first portion of the light toward an outer surface of a first layer of a multilayer sample in which the first layer may be oriented proximal to the beam splitter, the outer surface of the first layer positioned a first optical distance from the beam splitter. The method may also include directing, from the beam splitter, the second portion of the light onto a reflector positioned a second optical distance from the beam splitter. The method may further include combining, at the beam splitter, the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector. The method may also include directing, from the beam splitter, the combined light over the optical fiber. The method may further include receiving, at a computer-controlled system for analyzing Fabry-Perot fringes, the combined light over the optical fiber and spectrally analyzing the combined light using the system for analyzing Fabry-Perot fringes to determine a value of a total power impinging a slit of the system for analyzing Fabry-Perot fringes. Additionally or alternatively, the method may include receiving, at a computer-controlled spectrograph included in the system for analyzing Fabry-Perot fringes, the filtered light over the single-mode optical fiber, and spectrally analyzing the filtered light using the computer-controlled spectrograph to determine at least a first peak of a Fourier transform of the filtered light, the first peak created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light.

The method may also include determining the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light. The method may further include recording an interferogram that plots the value versus the OPD for the OPD. The method may also include performing the previous acts of the method one or more additional times after decreasing the first optical distance by moving the multilayer sample closer to the beam splitter, or after increasing the second optical distance by moving the reflector further away from the beam splitter, resulting in a different OPD. Additionally or alternatively, the method may include performing the previous acts of the method one or more additional times after inducing a different OPD that changes a frequency of at least the first peak to a new frequency. Based on one or more of the different OPDs and the new frequency of the first peak, the method may further include determining thicknesses and order of layers of the multilayer sample Additionally or alternatively, the method may further include using the interferogram for each of the different OPDs to determine the thicknesses and order of the layers of the multilayer sample.

In some embodiments, the method may further include receiving, at a directional element, the light from the broadband light source over the optical fiber and directing, from the directional element, the light to the beam splitter over the optical fiber. In some embodiments, the method may also include receiving, at the directional element, the combined light from the beam splitter and directing, from the directional element, the combined light to using the system for analyzing Fabry-Perot fringes. In some embodiments, the method may further include positioning the multilayer sample so that the first optical distance is shorter than the second optical distance by more than a coherence of the light emitted by the broadband light source. In some embodiments, the spectrally analyzing of the combined light at the system for analyzing Fabry-Perot fringes may be performed over all channels of the system for analyzing Fabry-Perot fringes. In some embodiments, the first optical distance may be decreased by an increment smaller than half of a wavelength of the first portion of the light. In some embodiments, the performing of the previous acts of the method may continue until the OPD is less than an anticipated optical thickness of the multilayer sample. In some embodiments, the method may further include positioning the multilayer sample so that the first optical distance is longer than the second optical distance by more than a coherence of the light emitted by the broadband light source.

Another embodiment may include a system for inspecting a multilayer sample. The system may include single mode optical fiber, a broadband light source, a beam splitter, a system for analyzing Fabry-Perot fringes, a motion stage, and a computer. The broadband light source may be configured to emit light over the optical fiber. The beam splitter may be configured to receive the light from the broadband light source and split the light into first and second portions, direct the first portion of the light toward an outer surface of a first layer of a multilayer sample in which the first layer may be oriented proximal to the beam splitter and the outer surface of the first layer may be positioned a first optical distance from the beam splitter, direct the second portion of the light onto a reflector positioned a second optical distance from the beam splitter, combine the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector, and direct the combined light over the optical fiber. The system for analyzing Fabry-Perot fringes may be configured to receive the combined light over the optical fiber and to spectrally analyze the combined light to measure a value of a total power impinging a slit of the system for analyzing Fabry-Perot fringes. Additionally or alternatively, the system for analyzing Fabry-Perot fringes may be configured to determine at least a first peak of a Fourier transform of the filtered light, the first peak created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light.

The motion stage may be configured to change a frequency of at least the first peak to a new frequency by changing one or both of the first optical distance and the second optical distance. Additionally or alternatively, the motion stage may be configured to decrease the first optical distance by moving the multilayer sample closer to the beam splitter or increase the second optical distance by moving the reflector further away from the beam splitter. The computer may be configured to control the system for analyzing Fabry-Perot fringes, determine the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light, record an interferogram that plots the value versus the OPD for each unique OPD, control the motion stage between measurements to change the OPD, and use the interferograms to determine the thicknesses and order of the layers of the multilayer sample. Additionally or alternatively, the computer may be configured to control the motion stage between measurements to change the OPD to a different OPD, and determine thicknesses and order of the layers of the multilayer sample based on the different OPD and the new frequency of at least the first peak.

In some embodiments, the system further includes a directional element configured to receive the light from the broadband light source over the optical fiber, direct the light to the beam splitter over the optical fiber, receive the combined light from the beam splitter, and direct the combined light to the system for analyzing Fabry-Perot fringes. In some embodiments, the system also includes a point detector configured to be employed when the system is operating in a Michelson interferometer mode and an optical switch configured to switch the combined light directed from directional element back and forth between the system for analyzing Fabry-Perot fringes and the point detector. In some embodiments, the system for analyzing Fabry-Perot fringes is configured to spectrally analyze the combined light over all channels of the system for analyzing Fabry-Perot fringes. In some embodiments, the computer may be configured to control the motion stage between measurements to only change the OPD by an increment smaller than half of a wavelength of the first portion of the light. In some embodiments, the computer may be configured to control the motion stage between measurements to change the OPD only until the OPD is less than an anticipated optical thickness of the multilayer sample.

It is to be understood that both the foregoing summary and the following detailed description are explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 illustrates a first example system for inspecting a multilayer sample;

FIG. 2 illustrates a second example system for inspecting a multilayer sample;

FIG. 3 illustrates a third example system for inspecting a multilayer sample;

FIG. 4 illustrates an example beam assembly that may be employed in the systems of FIGS. 1-3;

FIG. 5A illustrates an example multilayer sample oriented upside down;

FIG. 5B illustrates the example multilayer sample of FIG. 5A oriented right side up;

FIGS. 6A and 6B illustrate simulated Michelson interferograms of radiation that may be obtained by the systems of FIGS. 1-3 from the two example multilayer samples of FIGS. 5A and 5B, respectively;

FIGS. 6C and 6D illustrate simulated Fabry-Perot fringes interferograms that may be obtained from the two example multilayer samples of FIGS. 5A and 5B, respectively;

FIGS. 7A, 7B, 7C, and 7D are a flowchart of an example method for inspecting a multilayer sample; and

FIG. 8 illustrates an example system that may be used in the inspection of a multilayer sample.

DESCRIPTION OF EMBODIMENTS

Unlike conventional inspection systems, the embodiments disclosed herein may be able to correctly determine both the thicknesses and the order of the layers of a multilayer sample.

For example, during an automated manufacturing process, a multilayer wafer may have a silicon layer and a silicon dioxide layer, and the multilayer wafer may need to be oriented with the silicon layer on top to allow the silicon layer to be ground down during the automated manufacturing process to a specific thickness. The embodiments disclosed herein may be positioned above the multilayer wafer to inspect the multilayer wafer as it travels through the automated manufacturing process in order to measure the thickness of the top silicon layer to verify that the silicon layer is successfully ground down to the specific thickness. In this example, the multilayer wafer may inadvertently become turned upside down during the automated manufacturing process such that the silicon layer, which should be on the top to be exposed for grinding down, ends up on the bottom. The embodiments disclosed herein may be able to determine that the multilayer wafer has a top layer and a bottom layer, may be able to determine the thicknesses of the top layer and the bottom layer, and may be able to determine that the top layer is the silicon dioxide and the bottom layer is the silicon layer. Therefore, in this situation where the multilayer wafer inadvertently becomes turned upside down during the automated manufacturing process, the embodiments disclosed herein may be able to determine that there is a problem, which may avoid the silicon dioxide layer of the multilayer wafer being improperly ground down.

In another example, the use of systems that determine wafer thickness using spectral Fabry-Perot fringe analysis may measure only intensity of reflected radiation and may lose information about the change of the phase of the radiation during the reflection process. In contrast, interferometers may retain this phase information. Thus, interferograms collected by interferometers, such as Michelson interferometers, may contain more information than the intensity spectra. Therefore, embodiments disclosed herein may be employed to utilize a system that determines wafer thickness using spectral Fabry-Perot fringe analysis equipped with an additional reference mirror in order to collect interferograms.

Therefore, the embodiments disclosed herein may be able to correctly identify differences in the compositions of different layers of a multilayer sample during an automated manufacturing process. This ability of the embodiments disclosed herein may result in the detection of problems with the order of the layers in a multilayer sample, and the corresponding orientation of the layers, such as an upside-down multilayer sample, thereby avoiding manufacturing defects during the automated manufacturing process.

Embodiments of the present disclosure will be explained with reference to the accompanying drawings.

FIG. 1 illustrates a first example system 100 for inspecting a multilayer sample 500, arranged in accordance with at least some embodiments described in this disclosure. In general, the system 100 may be configured to inspect the multilayer sample 500 to correctly determine the number of layers, the thickness of each layer, the composition of each layer, the order of the layers, and the corresponding orientation of the layers. To perform the inspection, the system 100 may include single mode optical fibers 102-110, a broadband light source 112, a directional element 113, a beam splitter 114, a reflector 116, a system 118 for analyzing Fabry-Perot fringes and a computer 120.

In some embodiments, the broadband light source 112 may be configured to emit light over the optical fiber 102.

In some embodiments, the directional element 113 may be configured to receive the light from the broadband light source 112 and direct the light over the optical fiber 104 to the beam splitter 114.

In some embodiments, the beam splitter 114 may be configured to receive the light from the directional element 113 and split the light into first and second portions. The beam splitter 114 may also be configured to direct the first portion of the light over the optical fiber 106 toward the multilayer sample 500, for example, towards an outer surface of the multilayer sample 500 in which the outer surface may be oriented proximal to the beam splitter 114 and may be positioned a first optical distance D1 from the beam splitter 114. The beam splitter 114 may further be configured to direct the second portion of the light over the optical fiber 108 onto the reflector 116 positioned a second optical distance D2 from the beam splitter 114. The beam splitter 114 may also be configured to combine the first portion of the light after being reflected from the multilayer sample 500 and the second portion of the light after being reflected from the reflector 116. The beam splitter 114 may further be configured to direct the combined light over the optical fiber 104 back toward the directional element 113.

In some embodiments, the directional element 113 may be configured to receive the combined light from the beam splitter 114 and direct the combined light over the optical fiber 110 toward the system 118 for analyzing Fabry-Perot fringes.

In some embodiments, the system 118 for analyzing Fabry-Perot fringes may be configured to receive the combined light over the optical fiber 110. The system 118 for analyzing Fabry-Perot fringes may be further configured to spectrally analyze the combined light to measure a value of a total power impinging a slit of the system 118 for analyzing Fabry-Perot fringes. In these or other embodiments, the system 118 for analyzing Fabry-Perot fringes may be further configured to spectrally analyze the combined light to determine at least a first peak of a Fourier transform of the filtered light. The first portion of the light may follow a first optical path from the initial creation of the first portion at the beam splitter 114, to reflection off the outer surface, and then back to the beam splitter 114. Additionally, the second portion of the light may follow a second optical path from the initial creation of the second portion at the beam splitter 114 to the reflector 116 and then back to the beam splitter 114. The first peak may be created by an optical path difference (OPD) between the first optical path of the first portion of the light and the second optical path of the second portion of the light.

Additionally or alternatively, in some instances, the first optical path of the first portion of the light may be split into multiple sub-optical paths. For example, a first layer of the multilayer sample 500 that is an outer layer of the multilayer sample 500 and that includes the outer surface that is disposed proximal to the beam splitter 114 may be at least semi-transparent. As such, some of the first portion of the light may be reflected off the outer surface of the first layer toward the beam splitter 114. For example, some light of the first portion may follow a first sub-optical path from the beam splitter 114 to the outer surface and then back to the beam splitter 114. Additionally, some light of the first portion of the light may follow a second sub-optical path that passes through the first layer and reflects off a second layer that is disposed proximal to the first layer. In these or other embodiments, a first peak may be created based on the OPD between the first sub-optical path of the first portion of light and the second optical path of the second portion of the light. Additionally or alternatively, a second peak may be created based on the OPD between the second sub-optical path of the first portion of light and the second optical path of the second portion of the light. Note that the multilayer sample 500 may include one or more additional layers other than the first layer and the second layer and that one or more corresponding additional peaks may be created in a similar manner depending on the transparency of the second layer and the one or more additional layers.

In some embodiments, the system 118 for analyzing Fabry-Perot fringes may be configured to spectrally analyze the combined light over all channels of the system 118 for analyzing Fabry-Perot fringes.

In some embodiments, the system 118 for analyzing Fabry-Perot fringes may include a spectrometer. The spectrometer may include an array detector. The array detector of the spectrometer may include a spectral-detection range of about 200 nm to about 2000 nm. Additionally or alternatively, one or both of the spectrometer and the array detector may include a spectral resolution of about 0.002 nm to about 2 nm. In these or other embodiments, frequencies of peaks of the Fourier transform of the filtered light may be detected if within the spectral resolution of the spectrometer and/or the array detector. If within the spectral resolution of the spectrometer and/or the array detector, then the frequencies of the peaks may be analyzed and/or displayed, e.g., on a display of the system 118. For example, if an optical probe assembly including the beam splitter 114 and the reflector 116 is positioned too far from the multilayer sample 500, then the frequency of the peaks of the Fourier transform of the filtered light may be too large and therefore undetectable by the spectrometer and/or the array detector. Additionally, if the optical probe assembly is moved to a position closer to the multilayer sample 500, then the frequency of the peaks of the Fourier transform of the filtered light may decrease to a detectable threshold.

In some embodiments, the system 118 for analyzing Fabry-Perot fringes may include a spectrometer combined with an etalon filter. An example of the system 118 for analyzing Fabry-Perot fringes that combines a spectrometer with an etalon filter is disclosed in U.S. patent application Ser. No. 15/410,328, filed Jan. 19, 2017, which is incorporated herein by reference in its entirety.

In some embodiments, the system 100 may further include one or more motion stages (not shown) configured to reposition the reflector 116 and/or the multilayer sample 500 closer to, or further away from, the beam splitter 114. In some embodiments, the one or more motion stages may be configured to decrease the first optical distance D1 by moving the multilayer sample 500 closer to the beam splitter 114. In some embodiments, the one or more motion stages may be configured to increase the second optical distance D2 by moving the reflector 116 further away from the beam splitter 114. In some embodiments the one or more motion stages may be configured to both decrease the first optical distance D1 by moving the multilayer sample 500 closer to the beam splitter 114 as well as increase the second optical distance D2 by moving the reflector 116 further away from the beam splitter 114. Additionally or alternatively, during the motion stage, a new frequency of at least the first peak of the Fourier transform of the filtered light may be induced by one or more of: moving an optical probe assembly relative to the multilayer sample 500 to change the first optical distance D1, the optical probe assembly including at least the beam splitter 114 and the reflector 116; moving the multilayer sample relative to the beam splitter 114 to change the first optical distance D1; and moving the reflector 116 relative to the beam splitter to change the second optical distance D2.

In these or other embodiments, new frequencies of other peaks of the Fourier transform of the filtered light may also be induced, e.g., a second peak, a third peak, a fourth peak, and so forth, by changing one or more OPDs as described above. The other peaks may be related to one or more respective layers, interfaces, surfaces, etc. of the multilayer sample 500 and one or more OPDs associated therewith as discussed above.

In some embodiments, the system 100 may allow measurement of the first optical distance D1 and may be used to measure the topography, bow, and warp of the multilayer sample 500. In these or other embodiments, based on the one or more different OPDs and the new frequency of the first peak, the topography of the multilayer sample 500 may be determined. Additionally or alternatively, other peaks, including a frequency and/or period thereof, may be used to determine the topography of the multilayer sample 500. For example, a determined frequency difference between the new respective frequencies of the first peak and the second peak multiplied by a refractive index of a layer of interest in the multilayer sample 500 may approximately equal the thickness of the layer of interest. Additionally or alternatively, in some embodiments, determining the topography of the multilayer sample 500 may include one or more of: obtaining a reference measurement using an optically flat mirror; obtaining a plurality of sample measurements of the multilayer sample 500; and subtracting the reference measurement from the plurality of sample measurements.

In some embodiments, the computer 120 may be configured to control the system 118 for analyzing Fabry-Perot fringes, determine an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light, record an interferogram that plots the value versus the OPD for each unique OPD, control the motion stage between measurements to change the OPD, and use the interferograms to determine the thicknesses and order of the layers of the multilayer sample 500. In some embodiments, the computer 120 may be configured to control the one or more motion stages between measurements to only change the OPD by an increments smaller than half of a wavelength of the first portion of the light. In some embodiments, the computer may be configured to control the motion stage between measurements to change the OPD by an increment equal to or larger than half of a wavelength of the first portion of the light. In some embodiments, the computer 120 may be configured to control the one or more motion stages between measurements to change the OPD only until the OPD is less than an anticipated optical thickness of the multilayer sample 500.

In some embodiments, the computer 120 may be configured to control the system 118 for analyzing Fabry-Perot fringes, determine the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light, control the motion stage between measurements to change the OPD to a different OPD, and determine thicknesses and order of the layers of the multilayer sample 500 based on the different OPD and the new frequency of the first peak. Other peaks and associated frequencies created by different OPDs may be used to determine the thicknesses and the order of the layers of the multilayer sample 500.

In some embodiments, the computer 120 may include a processor and a memory. The processor may include, for example, a microprocessor, microcontroller, digital signal processor (DSP), application-specific integrated circuit (ASIC), a Field-Programmable Gate Array (FPGA), or any other digital or analog circuitry configured to interpret and/or to execute program instructions and/or to process data. In some embodiments, the processor may interpret and/or execute program instructions and/or process data stored in the memory. The processor may execute instructions to perform operations with respect to the system 118 for analyzing Fabry-Perot fringes and the one or more motion stages in order to determine the thicknesses and order of the layers of the multilayer sample 500. The memory may include any suitable computer-readable media configured to retain program instructions and/or data for a period of time. By way of example, and not limitation, such computer-readable media may include tangible and/or non-transitory computer-readable storage media including Random Access Memory (RAM), Read-Only Memory (ROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory devices (e.g., solid state memory devices), or any other storage medium which may be used to carry or store desired program code in the form of computer-executable instructions or data structures and which may be accessed by a general-purpose or special-purpose computer. Combinations of the above may also be included within the scope of computer-readable media. Computer-executable instructions may include, for example, instructions and data that cause a general-purpose computer, special-purpose computer, or special-purpose processing device to perform a certain function or group of functions.

The system 100 may be advantageously employed to inspect the multilayer sample 500 to correctly determine the number of layers, the thickness of each layer, the composition of each layer, the order of the layers, and the corresponding orientation of the layers. The system 100 may be advantageously employed in a variety of environments, such as an automated manufacturing process. For example, where the multilayer sample 500 includes a silicon layer and a silicon dioxide layer, and where it is important that the silicon layer be on top, the system 100 may be able to detect that the multilayer sample 500 is upside down as disclosed in FIG. 1, and thereby halt the automated manufacturing process until the orientation of the multilayer sample 500 is corrected in order to avoid manufacturing defects during the automated manufacturing process.

FIG. 2 illustrates a second example system 200 for inspecting the multilayer sample 500, arranged in accordance with at least some embodiments described in this disclosure. The system 200 of FIG. 2 is similar to the system 100 of FIG. 1, except that the system 200 eliminates the directional element 113, the beam splitter 114, and the optical fiber 104, and replaces these three components with a beam splitter/directional element 115. The beam splitter/directional element 115 of FIG. 2 combines the functionality of the directional element 113 and the beam splitter 114 of FIG. 1. Otherwise, the system 200 of FIG. 2 functions similarly to the system 100 of FIG. 1.

FIG. 3 illustrates a third example system 300 for inspecting the multilayer sample 500, arranged in accordance with at least some embodiments described in this disclosure. The system 300 of FIG. 3 is similar to the system 100 of FIG. 1, except that the system 300 adds an optical switch 122, optical fibers 124 and 126, and a point detector 128.

In some embodiments, the optical switch 122 may be controlled by the computer 120 and may be configured to switch the combined light directed from directional element 113 over the optical fiber 110 back and forth between the system 118 for analyzing Fabry-Perot fringes, over the optical fiber 124, and the point detector 128, over the optical fiber 126. The point detector 128 may be configured to be employed when the system 300 is operating in a Michelson interferometer mode, and may be controlled by the computer 120 in a similar manner as the system 118 for analyzing Fabry-Perot fringes is controlled by the computer 120.

For example, one may observe multiple reflections of light in single-layer and multilayer samples manifested in multiple interference peaks in Michelson interferograms. These reflections may be caused by multiple light reflections from various sample interfaces. Light may be reflected back and forth several times inside the sample before the light leaves the sample. These multiple scattering (reflection) paths may cause complications during Michelson interferogram analysis. By combining a Michelson interferometer with a Fabry-Perot interferometer, the analysis can be made easier. Fabry-Perot interferograms may help to determine the thicknesses of various layers residing in the samples faster and more accurately, while Michelson interferograms may help to determine their order (or sequence) relative to a probe head. An interferogram may contain more information about a sample since it contains information about phase and magnitude of the reflected electromagnetic wave from the sample, while the reflected spectrum intensity may only contain information about amplitude of the reflected radiation.

FIG. 4 illustrates an example beam assembly 400 that may be employed in the systems 100, 200, and 300 of FIGS. 1-3, arranged in accordance with at least some embodiments described in this disclosure. In particular, the beam assembly 400 may be employed in place of the beam splitter 114 and optical fibers 106 and 108 in the systems 100 and 300 of FIGS. 1 and 3, and may be employed in place of the beam splitter functionality of the beam splitter/directional element 115 and the optical fibers 106 and 108 of the system 200 of FIG. 2.

In some embodiments, the beam assembly 400 may include lenses 402 and 404. The beam assembly 400 may also include a beam splitter 406 and a reflector 408. The lens 402 may be configured to receiving the light over the optical fiber 102 or 104 and collimate and direct the light toward the beam splitter 406. The beam splitter 406 may be configured to split the light from the lens 402 into first and second portions, direct the first portion of the light toward the lens 404, and direct the second portion of the light onto the reflector 408. The lens 404 may be configured to receive the first portion of the light from the beam splitter 406, direct the first portion of the light toward the multilayer sample 500, and direct the first portion of the light after being reflected from the multilayer sample 500 back toward the beam splitter 406. Further, the reflector 408 may be configured to receive the second portion of the light from the beam splitter 406 and reflect the second portion of the light back toward the beam splitter 406. The beam splitter 406 may be further configured to combine the first portion of the light after being reflected from the multilayer sample 500 and the second portion of the light after being reflected from the reflector 408, and then direct the combined light toward the lens 402. Finally, the lens 402 may be configured to receive the combined light and direct the combined light over the optical fiber 102 or 104.

The beam assembly 400 may further include one or more motion stages (not shown) configured to reposition the reflector 408 and/or the multilayer sample 500 closer to, or further away from, the beam splitter 406, in order to adjust the optical distances D1 and D2, similarly to the one or more motion stages discussed above in connection with FIG. 1.

FIG. 5A illustrates the example multilayer sample 500 oriented upside down and FIG. 5B illustrates the example multilayer sample 500 oriented right-side up. In some embodiments, the multilayer sample 500 may be involved in an automated manufacturing process where it is important that the silicon layer be on top. Therefore, in this scenario, the multilayer sample 500 of FIG. 5A is upside down and the multilayer sample 500 of FIG. 5B is right-side up. The systems 100, 200, and 300 disclosed herein may be employed to detect that the multilayer sample 500 of FIG. 5A is upside down, and may thereby avoid manufacturing defects during the automated manufacturing process by halting the automated manufacturing process until the orientation of the multilayer sample 500 is corrected as disclosed in FIG. 5B.

FIGS. 6A and 6B illustrate simulated Michelson interferograms 600 a and 600 b of radiation that may be obtained by the systems 100, 200, and 300 of FIGS. 1-3 from the two orientations of the multilayer sample 500 of FIGS. 5A and 5B, respectively. FIGS. 6C and 6D illustrate simulated Fabry-Perot fringes interferograms 600 c and 600 d that may be obtained from the two example multilayer samples of FIGS. 5A and 5B, respectively. In contrast to the simulated Fabry-Perot fringes interferograms 600 c and 600 d of FIGS. 6C and 6D which appear identical, the simulated Michelson interferograms 600 a and 600 b appear different. As disclosed in the simulated Michelson interferograms 600 a and 600 b, the systems 100, 200, and 300 of FIGS. 1-3 may be able to distinguish between the silicon layer being on the top (as indicated in the simulated Michelson interferogram 600 a) and the silicon layer being on the bottom (as indicated in the simulated Michelson interferogram 600 b). Additionally, due to multiple reflections in the simulated Michelson interferograms 600 a and 600 b, the simulated Fabry-Perot interferograms 600 c and 600 d may be employed to help define the number of layers in the multilayer sample 500, while the simulated Michelson interferograms 600 a and 600 b may be employed to help define the order of the layers relative to the systems 100, 200, and 300 of FIGS. 1-3. Thus the thickness and order of the layers of the multilayer sample 500 of FIGS. 5A and 5B may be determined using the systems 100, 200, and 300 of FIGS. 1-3.

FIGS. 7A, 7B, 7C, and 7D are a flowchart of an example method 700 for inspecting a multilayer sample, arranged in accordance with at least some embodiments described in this disclosure. The method 700 may be implemented, in some embodiments, by a system, such as any of the systems 100, 200, and 300 of FIGS. 1, 2, and 3, respectively. Although illustrated as discrete blocks, various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation.

Block 702 may include emitting, from a broadband light source, light over single mode optical fiber. For example, the broadband light source 112 of FIG. 2 may emit, at block 702, light over the single mode optical fiber 102.

Block 704 may include receiving, at a beam splitter, the light and splitting, at the beam splitter, the light into first and second portions. For example, the beam splitter/directing element 115 of FIG. 2 may receive, at block 704, the light over the single mode optical fiber 102 and may split the light into first and second portions.

The block 706 may include directing, from the beam splitter, the first portion of the light toward a multilayer sample positioned a first optical distance from the beam splitter. For example, the beam splitter/directing element 115 of FIG. 2 may direct, at block 706, the first portion of the light over the optical fiber 106 toward an outer surface of a first layer of the multilayer sample 500 in which the first layer is oriented proximal to the beam splitter/directing element 115, the outer surface of the first layer positioned a first optical distance D1 from the beam splitter/directing element 115.

The block 708 may include directing, from the beam splitter, the second portion of the light onto a reflector positioned a second optical distance from the beam splitter. For example, the beam splitter/directing element 115 of FIG. 2 may direct, at block 708, the second portion of the light over the optical fiber 108 onto the reflector 116 positioned a second optical distance D2 from the beam splitter/directing element 115.

The block 710 may include combining, at the beam splitter, the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector. For example, the beam splitter/directing element 115 of FIG. 2 may combine, at block 710, the first portion of the light after being reflected from the multilayer sample 500 and the second portion of the light after being reflected from the reflector 116.

The block 712 may include directing, from the beam splitter, the combined light over the optical fiber. For example, the beam splitter/directing element 115 of FIG. 2 may direct, at block 712, the combined light over the optical fiber 110. In some embodiments, the method 700 may proceed from block 712 to block 714. Additionally or alternatively, in some embodiments, the method 700 may proceed from block 712 to block 727 described further below.

The block 714 may include receiving, at a computer-controlled system for analyzing Fabry-Perot fringes, the combined light over the optical fiber and spectrally analyzing the combined light using the system for analyzing Fabry-Perot fringes to determine a value of a total power impinging a slit of the system for analyzing Fabry-Perot fringes. For example, the system 118 for analyzing Fabry-Perot fringes of FIG. 2 may receive, at block 714, the combined light over the optical fiber 110 and spectrally analyze the combined light to determine a value of a total power impinging a slit of the system 118 for analyzing Fabry-Perot fringes. In some embodiments, the spectral analysis may be performed over all channels of the system for analyzing Fabry-Perot fringes.

The block 716 may include determining an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light. For example, the computer 120 of FIG. 2 may determine, at block 716, an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light.

The block 718 may include recording an interferogram that plots the value versus the OPD for the OPD. For example, the computer 120 of FIG. 2 may record, at block 718, an interferogram that plots the value versus the OPD for the OPD.

The decision block 720 may include determining whether the OPD is less than an anticipated optical thickness of the multilayer sample. If so (Yes at the decision block 720), the method may conclude with block 726. If not (No at decision block 720), the method may continue with either block 722 or block 724 and then return to block 702.

The block 722 may include decreasing the first optical distance by moving the multilayer sample closer to the beam splitter resulting in a different OPD. For example, the computer 120 of FIG. 2 may decrease, at block 722, the first optical distance D1 moving the multilayer sample 500, using a motion stage for example, closer to the beam splitter/directing element 115 resulting in a different OPD. In some embodiments, the first optical distance may be decreased at block 722 by an increment smaller than half of a wavelength of the first portion of the light.

The block 724 may include increasing the second optical distance by moving the reflector further away from the beam splitter resulting in a different OPD. For example, the computer 120 of FIG. 2 may increase, at block 724, the second optical distance D2 by moving the reflector 116, using a motion stage for example, further away from the beam splitter/directing element 115 resulting in a different OPD. In some embodiments, the second optical distance may be increased at block 724 by an increment smaller than half of a wavelength of the first portion of the light.

After a different OPD has been achieved in block 722 or block 724, the method may return to block 702 and repeat blocks 702-720 with the different OPD. This process may be iteratively repeated until the OPD is less than an anticipated optical thickness of the multilayer sample, at which point the method may continue to block 726.

Block 726 may include using the recorded interferogram for each of the different OPDs to determine the thicknesses and order of the layers of the multilayer sample. For example, the computer 120 of FIG. 2 may use, at block 726, the recorded interferogram for each of the different OPDs to determine the thicknesses and order of the layers of the multilayer sample 500. In this example, the computer 120 of FIG. 2 may determine that the top layer of the multilayer sample 500 is the silicon dioxide layer with a thickness of 10 microns (see FIG. 5A), and the bottom layer of the multilayer sample 500 is the silicon layer with a thickness of 120 microns (see FIG. 5A).

Block 727 may include receiving, at a computer-controlled etalon filter included in the system for analyzing Fabry-Perot fringes, the combined light, filtering the combined light at the computer-controlled etalon filter, directing, from the computer-controlled etalon filter, the filtered light over a single-mode optical fiber, receiving, at a computer-controlled spectrograph included in the system for analyzing Fabry-Perot fringes, the filtered light over the single-mode optical fiber, and spectrally analyzing the filtered light using the computer-controlled spectrograph to determine at least a first peak of a Fourier transform of the filtered light. In these or other embodiments, the first peak may be created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light. Additionally or alternatively, the first layer oriented proximal to the beam splitter may be an optically transparent layer in the multilayer sample. In some embodiments, the first layer may be a dicing tape, a grinding tape, or a silicon layer.

Block 728 may include determining the OPD between an optical path of the first portion of the light and an optical path of the second portion of the light. For example, the computer 120 of FIG. 2 may determine, at block 728, an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light. In these or other embodiments, the optical path of the first portion of the light may split into multiple sub-optical paths at the outer surface of the first layer of the multilayer sample. For example, the outer surface of the first layer may be semi-transparent. In these or other embodiments, some light of the first portion may be reflected off the outer surface of the first layer toward the beam splitter. As such, some of the first portion of light may follow a first sub-optical path of the first portion of light from the beam splitter to the outer surface and then back to the beam splitter. Additionally, some light of the first portion of the light may follow a second sub-optical path that passes through the first layer and reflects off a second layer that is disposed proximal to the first layer. In these or other embodiments, a first peak may be created based on the OPD between the first sub-optical path of the first portion of light and the second optical path of the second portion of the light. Additionally or alternatively, a second peak may be created based on the OPD between the second sub-optical path of the first portion of the light and the second optical path of the second portion of the light.

Block 730 may include inducing a different OPD that changes a frequency of at least the first peak to a new frequency. After inducing the different OPD that changes the frequency of at least the first peak to the new frequency, blocks 702-712 and 727-730 may be repeated one or more additional times.

In these or other embodiments, inducing the different OPD that changes the frequency of at least the first peak may include one or more of: moving an optical probe assembly, e.g., a proximal optical probe and/or a distal optical probe, relative to the multilayer sample to change the first optical distance, the optical probe assembly including at least the beam splitter and the reflector; moving the multilayer sample relative to the beam splitter to change the first optical distance; and moving the reflector relative to the beam splitter to change the second optical distance.

Additionally or alternatively, block 730 may include performing blocks 702-712 and 727-730 one or more additional times after inducing the different OPD that changes the frequency of a second peak of the Fourier transform of the filtered light to a new frequency, the second peak created by an OPD between the second sub-optical path of the optical path of the first portion of the light (discussed above in conjunction with block 728) and the optical path of the second portion of the light. In some embodiments, after inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the different OPD may be smaller than the OPD prior to the changed frequency of the first peak. In these or other embodiments, prior to inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the first peak may be undetectable, e.g., by an array detector of the computer-controlled spectrograph. Additionally or alternatively, after inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the first peak may be detectable, e.g., by the array detector of the computer-controlled spectrograph. Thus, in some embodiments, inducing the different OPD that changes the frequency of at least the first peak to the new frequency may be based on a spectral resolution of one or both of the computer-controlled spectrograph and the array detector.

Block 732 may include, based on one or more of the different OPDs and the new frequency of the first peak, determining thicknesses and order of layers of the multilayer sample. In some embodiments, determining the thicknesses and the order of the layers of the multilayer sample may include determining a difference between the frequency of the first peak and the second peak described above in conjunction with block 730. For example, the determined difference between the new respective frequencies of the first peak and the second peak multiplied by a refractive index of the layer of interest may approximately equal the thickness of the layer of interest. Additionally or alternatively, based on the one or more different OPDs and the new frequency of at least the first peak, block 732 may include determining a topography of the multilayer sample. In these or other embodiments, determining the topography of the multilayer sample may include one or more of: obtaining a reference measurement using an optically flat mirror; obtaining a plurality of sample measurements of the multilayer sample; and subtracting the reference measurement from the plurality of sample measurements.

In these or other embodiments, the method 700 may be performed via a proximal optical probe assembly positioned proximal to the outer surface of the first layer, the proximal optical probe assembly including at least the beam splitter and the reflector. Additionally or alternatively, other probe assemblies may be used and suitably positioned, for example, a distal optical probe assembly positioned opposite the outer surface of the first layer. In some instances, such as a two-layered multilayer sample, the first peak described in blocks 727, 730, and 732 performed via the distal optical probe assembly may correspond to an outer surface of the second layer.

One skilled in the art will appreciate that, for this and other methods disclosed in this disclosure, the blocks of the methods may be implemented in differing order. Furthermore, the blocks are only provided as examples, and some of the blocks may be optional, combined into fewer blocks, or expanded into additional blocks.

For example, in some embodiments, an additional block may be included in the method 700 that includes positioning the multilayer sample so that the first optical distance is shorter than the second optical distance by more than a coherence of the light emitted by the broadband light source. For example, the multilayer sample 500 of FIG. 2 may be positioned prior to block 702 so that the first optical distance D1 is shorter than the second optical distance D2 by more than a coherence of the light emitted by the broadband light source 112.

Further, in some embodiments, an additional block may be included in the method 700 that includes positioning the multilayer sample so that the first optical distance is longer than the second optical distance by more than a coherence of the light emitted by the broadband light source. For example, the multilayer sample 500 of FIG. 2 may be positioned prior to block 702 so that the first optical distance D1 is longer than the second optical distance D2 by more than a coherence of the light emitted by the broadband light source 112.

In these or other embodiments, one or more blocks of the method 700 may be modified. For example, either of the proximal optical probe assembly or the distal optical probe assembly may perform blocks 702-712 and 727-730 one or more additional times after inducing the different OPD that changes a frequency of the second peak of the Fourier transform of the filtered light to the new frequency. The second peak may be created by an OPD between the second sub-optical path of the optical path of the first portion of the light (discussed above in conjunction with block 728) and the optical path of the second portion of the light.

Additionally or alternatively, a block may be included in the method 700 that includes determining a thickness of one or both of the first layer and the second layer. For example, in the embodiment that includes the proximal optical probe and the distal optical probe, two first peaks may be identified corresponding to the respective outer surfaces of the first layer and the second layer. Additionally or alternatively, a second peak may be identified that relates to the interface between the first layer and the second layer. Based on the first peaks relating to the respective outer surfaces of the first layer and the second layer, and based on the second peak relating to the interface between the first layer and the second layer, a block in the method 700 may include determining a thickness of one or both of the first layer and the second layer.

Additionally or alternatively, a block may be included in the method 700 that includes identifying peaks beyond the first peak and the second peak. In some embodiments, peaks of the Fourier transform of the filtered light beyond the first peak and the second peak may be difficult to identify. In these or other embodiments, filtering methods and other suitable methods may be employed to analyze the peaks beyond the first peak and the second peak. Additionally or alternatively, a relationship of peaks, such as the first peak and the second peak, relative to stationary Fabry Perot peaks may be determined and/or analyzed.

FIG. 8 illustrates an example system 800 that may be used in the inspection of a multilayer sample. The system 800 may be arranged in accordance with at least one embodiment described in the present disclosure. The system 800 may include a processor 810, memory 812, a communication unit 816, a display 818, a user interface unit 820, and a peripheral device 822, which all may be communicatively coupled. In some embodiments, the system 800 may be part of any of the systems or devices described in this disclosure.

Generally, the processor 810 may include any suitable special-purpose or general-purpose computer, computing entity, or processing device including various computer hardware or software modules and may be configured to execute instructions stored on any applicable computer-readable storage media. For example, the processor 810 may include a microprocessor, a microcontroller, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a Field-Programmable Gate Array (FPGA), or any other digital or analog circuitry configured to interpret and/or to execute program instructions and/or to process data.

Although illustrated as a single processor in FIG. 8, it is understood that the processor 810 may include any number of processors distributed across any number of networks or physical locations that are configured to perform individually or collectively any number of operations described in this disclosure. In some embodiments, the processor 810 may interpret and/or execute program instructions and/or process data stored in the memory 812. In some embodiments, the processor 810 may execute the program instructions stored in the memory 812.

For example, in some embodiments, the processor 810 may execute program instructions stored in the memory 812 that are related to determining whether generated sensory data indicates an event and/or determining whether the event is sufficient to determine that the user is viewing a display of a device such that the system 800 may perform or direct the performance of the operations associated therewith as directed by the instructions. In these and other embodiments, instructions may be used to perform one or more operations of the methods described in the present disclosure.

The memory 812 may include computer-readable storage media or one or more computer-readable storage mediums for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable storage media may be any available media that may be accessed by a general-purpose or special-purpose computer, such as the processor 810. By way of example, and not limitation, such computer-readable storage media may include non-transitory computer-readable storage media including Random Access Memory (RAM), Read-Only Memory (ROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory devices (e.g., solid state memory devices), or any other storage medium which may be used to carry or store particular program code in the form of computer-executable instructions or data structures and which may be accessed by a general-purpose or special-purpose computer. Combinations of the above may also be included within the scope of computer-readable storage media. Computer-executable instructions may include, for example, instructions and data configured to cause the processor 810 to perform a certain operation or group of operations as described in this disclosure. In these and other embodiments, the term “non-transitory” as explained in the present disclosure should be construed to exclude only those types of transitory media that were found to fall outside the scope of patentable subject matter in the Federal Circuit decision of In re Nuijten, 500 F.3d 1346 (Fed. Cir. 2007). Combinations of the above may also be included within the scope of computer-readable media.

The communication unit 816 may include any component, device, system, or combination thereof that is configured to transmit or receive information over a network. In some embodiments, the communication unit 816 may communicate with other devices at other locations, the same location, or even other components within the same system. For example, the communication unit 816 may include a modem, a network card (wireless or wired), an infrared communication device, a wireless communication device (such as an antenna), and/or chipset (such as a Bluetooth device, an 802.6 device (e.g., Metropolitan Area Network (MAN)), a Wi-Fi device, a WiMax device, cellular communication facilities, etc.), and/or the like. The communication unit 816 may permit data to be exchanged with a network and/or any other devices or systems described in the present disclosure.

The display 818 may be configured as one or more displays, like an LCD, LED, or other type of display. For example, the display 818 may be configured to present measurements, indicate warning notices, show tolerance ranges, display whether proper configuration or placement of samples is satisfied, and other data as directed by the processor 810.

The user interface unit 820 may include any device to allow a user to interface with the system 800. For example, the user interface unit 820 may include a mouse, a track pad, a keyboard, buttons, and/or a touchscreen, among other devices. The user interface unit 820 may receive input from a user and provide the input to the processor 810. In some embodiments, the user interface unit 820 and the display 818 may be combined.

The peripheral devices 822 may include one or more devices. For example, the peripheral devices may include a sensor, a microphone, and/or a speaker, among other peripheral devices. As examples, the sensor may be configured to sense changes in light, sound, motion, rotation, position, orientation, magnetization, acceleration, tilt, vibration, etc. of a multilayer sample. Additionally or alternatively, the sensor may be part of or communicatively coupled to a spectrometer as described in the present disclosure.

Modifications, additions, or omissions may be made to the system 800 without departing from the scope of the present disclosure. For example, in some embodiments, the system 800 may include any number of other components that may not be explicitly illustrated or described. Further, depending on certain implementations, the system 800 may not include one or more of the components illustrated and described.

Terms used in this disclosure and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes, but is not limited to,” etc.).

Additionally, if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” or “one or more of A, B, and C, etc.” is used, in general such a construction is intended to include A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, etc. For example, the use of the term “and/or” is intended to be construed in this manner.

Further, any disjunctive word or phrase presenting two or more alternative terms, whether in the description of embodiments, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” should be understood to include the possibilities of “A” or “B” or “A and B.”

All examples and conditional language recited in this disclosure are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for inspecting a multilayer sample, the method comprising: (b) emitting light from a broadband light source; (c) receiving, at a beam splitter, the light and splitting, at the beam splitter, the light into first and second portions; (d) directing, from the beam splitter, the first portion of the light toward an outer surface of a first layer of a multilayer sample in which the first layer is oriented proximal to the beam splitter, the outer surface of the first layer positioned a first optical distance from the beam splitter; (e) directing, from the beam splitter, the second portion of the light onto a reflector positioned a second optical distance from the beam splitter; (f) combining, at the beam splitter, the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector; (g) directing, from the beam splitter, the combined light toward a system for analyzing Fabry-Perot fringes; (h) receiving, at a computer-controlled etalon filter included in the system for analyzing Fabry-Perot fringes, the combined light, filtering the combined light at the computer-controlled etalon filter, directing, from the computer-controlled etalon filter, the filtered light over a single-mode optical fiber, receiving, at a computer-controlled spectrograph included in the system for analyzing Fabry-Perot fringes, the filtered light over the single-mode optical fiber, and spectrally analyzing the filtered light using the computer-controlled spectrograph to determine at least a first peak of a Fourier transform of the filtered light, the first peak created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light; (i) determining the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light; (j) performing (b)-(i) one or more additional times after inducing a different OPD that changes a frequency of at least the first peak to a new frequency; and (k) based on one or more of the different OPDs and the new frequency of the first peak, determining thicknesses and order of layers of the multilayer sample.
 2. The method of claim 1, wherein inducing the different OPD that changes the frequency of at least the first peak includes one or more of: moving an optical probe assembly relative to the multilayer sample to change the first optical distance, the optical probe assembly including at least the beam splitter and the reflector; moving the multilayer sample relative to the beam splitter to change the first optical distance; and moving the reflector relative to the beam splitter to change the second optical distance.
 3. The method of claim 1, wherein: the optical path of the first portion of the light splits at the outer surface of the first layer of the multilayer sample, the optical path of the first portion splitting into at least two sub-optical paths including a first sub-optical path that reflects off the outer surface of the first layer and a second sub-optical path that proceeds through the first layer and reflects off an interface between the first layer and a second layer of the multilayer sample in which the second layer is oriented proximal to the first layer; and (j) further comprises performing (b)-(i) one or more additional times after inducing the different OPD that changes a frequency of a second peak of the Fourier transform of the filtered light to a new frequency, the second peak created by an OPD between the second sub-optical path of the optical path of the first portion of the light and the optical path of the second portion of the light.
 4. The method of claim 3, wherein determining the thicknesses and the order of the layers of the multilayer sample includes determining a frequency difference between the first peak and the second peak.
 5. The method of claim 1, wherein the first layer oriented proximal to the beam splitter is an optically transparent layer in the multilayer sample.
 6. The method of claim 5, wherein the first layer is a dicing tape, a grinding tape, or a silicon layer.
 7. The method of claim 1, wherein after inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the different OPD is smaller than the OPD prior to the changed frequency of at least the first peak.
 8. The method of claim 7, wherein: prior to inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the first peak is undetectable; and after inducing the different OPD that changes the frequency of at least the first peak to the new frequency, the first peak is detectable.
 9. The method of claim 1, wherein the computer-controlled spectrograph includes an array detector.
 10. The method of claim 9, wherein inducing the different OPD that changes the frequency of at least the first peak to the new frequency is based on a spectral resolution of one or both of the computer-controlled spectrograph and the array detector.
 11. The method of claim 1, further comprising: based on the one or more different OPDs and the new frequency of at least the first peak, determining a topography of the multilayer sample.
 12. The method of claim 11, wherein determining the topography of the multilayer sample includes: obtaining a reference measurement using an optically flat mirror; obtaining a plurality of sample measurements of the multilayer sample; and subtracting the reference measurement from the plurality of sample measurements.
 13. The method of claim 1, wherein (b)-(k) are performed via a proximal optical probe assembly positioned proximal to the outer surface of the first layer, the proximal optical probe assembly including at least the beam splitter and the reflector, and the method further comprises: performing (b)-(k) via a distal optical probe assembly positioned opposite the outer surface of the first layer, wherein the first peak of (h), (j), and (k) performed via the distal optical probe assembly corresponds to an outer surface of the second layer.
 14. The method of claim 13, wherein the optical path of the first portion of the light splits at the outer surface of the first layer of the multilayer sample, the optical path of the first portion splitting into at least two sub-optical paths including a first sub-optical path that reflects off the outer surface of the first layer and a second sub-optical path that proceeds through the first layer and reflects off an interface between the first layer and a second layer of the multilayer sample in which the second layer is oriented proximal to the first layer; and the method further comprises: via either of the proximal optical probe assembly or the distal optical probe assembly, performing (b)-(i) one or more additional times after inducing the different OPD that changes a frequency of a second peak of the Fourier transform of the filtered light to a new frequency, the second peak created by an OPD between the second sub-optical path of the first portion of the light and the optical path of the second portion of the light, the second peak corresponding to an interface between the first layer and the second layer of the multilayer sample.
 15. The method of claim 14, further comprising: based on the first peaks corresponding to the respective outer surfaces of the first layer and the second layer, and based on the second peak corresponding to the interface between the first layer and the second layer, determining a thickness of one or both of the first layer and the second layer.
 16. A system for inspecting a multilayer sample, the system comprising: a broadband light source configured to emit light; a beam splitter configured to receive the light from the broadband light source and split the light into first and second portions, direct the first portion of the light toward an outer surface of a first layer of a multilayer sample in which the first layer is oriented proximal to the beam splitter and the outer surface of the first layer is positioned a first optical distance from the beam splitter, direct the second portion of the light onto a reflector positioned a second optical distance from the beam splitter, combine the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector, and direct the combined light toward a system for analyzing Fabry-Perot fringes; the system for analyzing Fabry-Perot fringes configured to receive, at a computer-controlled etalon filter, the combined light, filter the combined light at the computer-controlled etalon filter, direct, from the computer controlled-etalon filter, the filtered light over a single-mode optical fiber, receive at a computer-controlled spectrograph included in the system for analyzing Fabry-Perot fringes, the filtered light over the single-mode optical fiber, and spectrally analyze the filtered light, using the computer-controlled spectrograph, to determine at least a first peak of a Fourier transform of the filtered light, the first peak created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light; a motion stage configured to change a frequency of at least the first peak to a new frequency by changing one or both of the first optical distance and the second optical distance; and a computer configured to control the system for analyzing Fabry-Perot fringes, determine the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light, control the motion stage between measurements to change the OPD to a different OPD, and determine thicknesses and order of the layers of the multilayer sample based on the different OPD and the new frequency of at least the first peak.
 17. The system of claim 16, wherein during the motion stage, the frequency change of at least the first peak is induced by one or more of: moving an optical probe assembly relative to the multilayer sample to change the first optical distance, the optical probe assembly including at least the beam splitter and the reflector; moving the multilayer sample relative to the beam splitter to change the first optical distance; and moving the reflector relative to the beam splitter to change the second optical distance.
 18. The system of claim 17, wherein: the optical path of the first portion of the light splits at the outer surface of the first layer of the multilayer sample, the optical path of the first portion splitting into at least two sub-optical paths including a first sub-optical path that reflects off the outer surface of the first layer and a second sub-optical path that proceeds through the first layer and reflects off an interface between the first layer and a second layer of the multilayer sample in which the second layer is oriented proximal to the first layer; and during the motion stage, a frequency change is induced of a second peak of the Fourier transform of the filtered light to a new frequency, the second peak created by an OPD between the second sub-optical path of the optical path of the first portion of the light and the optical path of the second portion of the light.
 19. The system of claim 18, wherein determining the thicknesses and the order of the layers of the multilayer sample includes determining a relationship between the new respective frequencies of the first peak and the second peak.
 20. The system of claim 16, wherein after the motion stage, the different OPD is smaller than the OPD prior to the changed frequency of at least the first peak. 